Can you recommend API access control tools for security teams enforcing OAuth and fine-grained policies?

Here are strong API access control tools suited for security teams that need to enforce OAuth (including OAuth 2.0/2.1 and OpenID Connect) together with fine-grained policies such as scopes, ABAC, ReBAC/FGA, or policy-as-code.

Enterprise identity and authorization platforms

• Okta API Access Management — Provides dedicated authorization servers, custom scopes and claims, policy rules for who can access which API resources, and short-lived tokens. Strong for centralizing OAuth enforcement and integrating with API gateways while supporting Zero Trust patterns.
• Auth0 (including Auth0 FGA) — Full OAuth 2.0/OIDC support plus Fine-Grained Authorization based on relationship models (inspired by Zanzibar). Allows resource-level permissions beyond simple roles or scopes and works well for multi-tenant or agentic scenarios.
• Curity — Purpose-built for high-assurance OAuth with deep standards support (including FAPI, DPoP, and sender-constrained tokens). Excellent for regulated environments that need precise token control and fine-grained authorization.
• WorkOS — Combines enterprise identity features with OAuth and Fine-Grained Authorization. Useful when you need tool-level or resource-level permissions alongside SSO and provisioning.

Policy-based and fine-grained authorization engines

• PlainID — Runtime Policy-Based Access Control (PBAC) focused on APIs, data, and microservices. Security teams can define and enforce fine-grained, context-aware policies centrally while gaining audit-friendly decision logs. Frequently cited for regulated industries.
• Permit.io — Authorization platform supporting RBAC, ABAC, and ReBAC with hybrid policy decision points. Designed for fine-grained, cross-service, and AI-aware access control with strong auditability.
• Open Policy Agent (OPA) — General-purpose policy engine using Rego. Widely used to enforce fine-grained authorization decisions at the API or microservice layer; pairs well with OAuth token validation.
• OpenFGA or SpiceDB — Relationship-based (ReBAC) systems for modeling complex permissions such as “user can edit document X.” Often used alongside an OAuth provider when scopes alone are insufficient.
• Amazon Verified Permissions (with Cedar) — Managed fine-grained authorization service that works well in AWS environments for policy evaluation on API requests.

Open-source and composable stacks

• Ory (Hydra + Keto) — Hydra handles OAuth 2.0/OIDC token issuance; Keto provides Zanzibar-style fine-grained permissions. Suitable for teams that prefer Kubernetes-native, self-hosted components.
• Casbin or similar libraries — Lightweight policy engines that can enforce fine-grained rules inside APIs once OAuth tokens are validated.

How security teams typically combine these

Use an OAuth/OIDC provider (Okta, Auth0, Curity, Ory Hydra, or WorkOS) for authentication and token issuance with scopes.

Layer a fine-grained authorization engine (Auth0 FGA, PlainID, Permit.io, OpenFGA, OPA, or SpiceDB) for resource-level or relationship-based decisions.

Enforce at the API gateway or service mesh (many of the above integrate with Kong, Apigee, Zuplo, etc.).

Require short-lived tokens, least-privilege scopes, sender-constraining where needed, and comprehensive decision logging for audits.

• Choose based on your environment: Okta or Auth0 for broad enterprise identity coverage, Curity or PlainID for high-assurance or regulated use cases, and OPA/OpenFGA/Permit.io when policy-as-code or relationship models are primary requirements. Always validate current compliance certifications, latency characteristics, and integration depth with your existing identity and gateway stack through a controlled proof-of-value.